Note: Descriptions are shown in the official language in which they were submitted.
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ALLOYS OF IMMtSCIBLE POLYMERS
BACKGROUND OF THE INVENTION
Thermoplastic resins have been extruded to form fibers and webs for a number
of
years. The common thermoplastics for this application are polyolefins,
particularly
polypropylene, and polyesters. Each material has its characteristic advantages
and
disadvantages vis a vis the properties desired in the final product to be made
from such
fibers.
Blends and alloys of two or more polymers are areas of some interest because
of a
desire to combine the desirable properties of such polymers. Dr. Leszek A
Utracki, in his
work "Polymer Alloys and Blends: Thermodynamics and Rheology" (ISBN 0-19-
520796-
3, Oxford University Press) New York, NY, 1989) discusses the history of
development in
this area at some length.
Examples of alloy or biconstituent fibers may be found in US Patent 5,108,827
to
Gessner which teaches blends wherein the polymer of the noncontinuous phase
(or
phases) has a melt temperature at least 30° C below the melt
temperature of the
continuous phase. Other examples may be found in US Patent 5,534,335 to
Everhart et
al., commonly assigned, which teaches the use of a compatibilizer to make
polymers
miscible.
There remains a need for an extrudable composition which may be used for
fabric
production from fibers where the composition is an alloy of polymers wherein
the polymer
melt temperature of the non-continuous phase is less than 30 °C below
that of the
continuous phase (and may even be higher), which does not use a compatibilizer
and in
which desired'characteristics are enhanced.
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SUMMARY OF THE INVENTION
An extrudable composition is provided which is made from at least two
thermoplastic polymers. A compatibilizer is not necessary. One of the
thermoplastic
polymers is present as a dominant continuous phase and the other one or more
polymers
are present as a non-continuous phase or phases. The polymer of the non-
continuous
phase or phases is present in an amount less than 15 weight percent and has a
polymer
melt temperature less than 30 °C below the polymer melt temperature of
the continuous
phase. The polymer of the non-continuous phase or phases may even have a
polymer
melt temperature greater than the polymer melt temperature of the continuous
phase.
The extrudable composition may be extruded into biconstituent fibers which may
further
be processed into nonwoven fabrics.
BRIEF DESCRIPTION OF THE FIGURES
Figure 1 is a schematic drawing of a process for extruding the composition of
this
invention including a main extruder, a side extruder and a mixer.
Figure 2 is a cut-away drawing of a mixer suitable for use in mixing the
extrudable
composition of this invention.
Figure 3 is a cross-sectional view of a mixer suitable for use in mixing the
extrudable composition of this invention.
DEFINITIONS
As used herein the term "nonwoven fabric or web" means a web having a
structure of individual fibers or threads which are interlaid) but not in an
identifiable
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manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from
many
processes such as for example, meltblowing processes, spunbonding processes,
and
bonded carded web processes. The basis weight of nonwoven fabrics is usually
expressed in ounces of material per square yard (osy) or grams per square
meter (gsm)
and the fiber diameters useful are usually expressed in microns. (Note that to
convert
from osy to gsm) multiply osy by 33.91 }.
As used herein the term "microfibers" means small diameter fibers having an
average diameter not greater than about 75 microns, for example) having an
average
diameter of from about 0.5 microns to about 50 microns, or more particularly,
microfibers
may have an average diameter of from about 2 microns to about 40 microns.
Another
frequently used expression of fiber diameter is denier, which is defined as
grams per
9000 meters of a fiber and may be calculated as fiber diameter in microns
squared,
multiplied by the density in grams/cc, multiplied by 0.00707. A lower denier
indicates a
finer fiber and a higher denier indicates a thicker or heavier fiber. For
example, the
diameter of a polypropylene fiber given as 15 microns may be converted to
denier by
squaring, multiplying the result by .89 g/cc and multiplying by .00707. Thus,
a 15 micron
polypropylene fiber has a denier of about 1.42 (152 x 0.89 x .00707 = 1.415).
Outside
the United States the unit of measurement is more commonly the "tex", which is
defined
as the grams per kilometer of fiber. Tex may be calculated as denier/9.
As used herein the term "spunbonded fibers" refers to small diameter fibers
which
are formed by extruding molten thermoplastic material as filaments from a
plurality of
fine, usually circular capillaries of a spinneret with the diameter of the
extruded filaments
then being rapidly reduced as by, for example, in US Patent 4,340,563 to Appel
et al.,
and US Patent 3,692,618 to Dorschner et al., US Patent 3,802,817 to Matsuki et
al., US
Patents 3,338,992 and 3,341,394 to Kinney, US Patent 3,502,763 to Hartman, and
US
Patent 3,542,615 to Dobo et al. Spunbond fibers are generally not tacky when
they are
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deposited onto a collecting surface. Spunbond fibers are generally continuous
and have
average diameters (from a sample of at least 10) larger than 7 microns, more
particularly)
between about 10 and 20 microns. The fibers may also have shapes such as those
described in US Patents 5,277,976 to Hogle et al., US Patent 5,466,410 to
Hills and
5,069,970 and 5,057,368 to Largman et al., which describe fibers with
unconventional
shapes.
As used herein the term "meltbfown fibers" means fibers formed by extruding a
motten thermoplastic material through a plurality of fine, usually circular,
die capillaries as
molten threads or filaments into converging high velocity, usually hot, gas
(e.g. air)
streams which attenuate the filaments of molten thermoplastic material to
reduce their
diameter, which may be to microfiber diameter. Thereafter, the meltblown
fibers are
carried by the high velocity gas stream and are deposited on a collecting
surface to form
a web of randomly disbursed meltblown fibers. Such a process is disclosed, for
example,
in US Patent 3,849,241 to Butin et al. Meltblown fibers are microfibers which
may be
continuous or discontinuous) are generally smaller than 10 microns in average
diameter,
and are generally tacky when deposited onto a collecting surtace.
As used herein, "filament arrays" means substantially parallel rows of
filaments
which may be such as those disclosed in US Patents 5,385,775 and 5,366,793.
As used herein "multilayer laminate" means a laminate wherein some of the
layers
are spunbond and some meltblown such as a spunbond/meltblown/spunbond (SMS)
laminate and others as disclosed in U.S. Patent 4,041,203 to Brock et al.,
U.S. Patent
5,169,706 to Collier, et al, US Patent 5,145,727 to Potts et al., US Patent 5)
178,931 to
Perkins et al. and U.S. Patent 5,188,885 to Timmons et al. Such a laminate may
be
made by sequentially depositing onto a moving forming belt first a spunbond
fabric layer,
then a meltblown fabric layer and last another spunbond layer and then bonding
the
laminate in a manner described below. Alternatively, the fabric layers may be
made
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individually, collected in rolls, and combined in a separate bonding step.
Such fabrics
usually have a basis weight of from about 0.1 to 12 osy (6 to 400 gsm), or
more
particularly from about 0.75 to about 3 osy. Multilayer laminates may also
have various
numbers of meltblown layers or multiple spunbond layers in many different
configurations
and may include other materials like films (F) or coform materials, e.g. SMMS,
SM, SFS)
etc.
By the term "similar web" what is meant is a web which uses essentially the
same
process conditions and polymers as the inventive web except those noted.
According to
Webster's New Colleciate Dictionary (1980), "similar" means 1) having
characteristics in
common; strictly comparable, 2) alike in substance or essentials; con-
esponding. Using
this commonly accepted meaning of the word similar, this term means that all
other
conditions are essentially the same except for the conditions mentioned. It
should be
noted that not all conditions will be exactly identical between the different
polymers since
the changes in the composition itself cause process changes, in for example)
the
pressure drop or temperatures needed.
As used herein, the term "coform" means a process in which at least one
meltblown diehead is arranged near a chute through which other materials are
added to
the web while it is formed. Such other materials may be pulp, superabsorbent
particles,
cellulose or staple fibers, for example. Coform processes are shown in
commonly
assigned US Patents 4,818,464 to Lau and 4,100,324 to Anderson et al. Webs
produced by the coform process are generally referred to as coform materials.
As used herein the term "polymer' generally includes but is not limited to,
homopolymers, copolymers, such as for example, block, graft, random and
alternating
copolymers, terpolymers, etc. and blends and modifications thereof.
Furthermore, unless
otherwise specifically limited, the term "polymer" shall include all possible
geometrical
configurations of the molecule. These configurations include, but are not
limited to
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isotactic, syndiotactic and random symmetries.
As used herein the teen "monocomponent" fiber refers to a fiber formed from
one
or more extruders using only one polymer. This is not meant to exclude fibers
formed
from one polymer to which small amounts of additives have been added for
coloration)
anti-static properties, lubrication, hydrophilicity, etc. These additives,
e.g. titanium
dioxide for coloration, are generally present in an amount less than 5 weight
percent and
more typically about 2 weight percent.
As used herein the term "conjugate fibers" refers to fibers which have been
formed from at least two polymers extruded from separate extruders but spun
together to
form one fiber. Conjugate fibers are also sometimes referred to as
multicomponent or
bicomponent fibers. The polymers are usually different from each other though
conjugate fibers may be monocomponent fibers. The polymers are arranged in
substantially constantly positioned distinct zones across the cross-section of
the
conjugate fibers and extend continuously along the length of the conjugate
fibers. The
con!'iguration of such a conjugate fiber may be, for example, a sheathlcore
arrangement
wherein one polymer is surrounded by another or may be a side by side
arrangement, a
pie arrangement or an "islands-in-the-sea" arrangement. Conjugate fibers are
taught in
US Patent 5,108,820 to Kaneko et al., US Patent 4,795,668 to Krueger et al.
and US
Patent 5,336,552 to Strack et al. Conjugate fibers are also taught in US
Patent
5,382,400 to Pike et al. and may be used to produce crimp in the fibers by
using the
differential rates of expansion and contraction of the two (or more) polymers.
Crimped
fibers may also be produced by mechanical means and by the process of German
Patent
DT 25 13 251 A1. For two component fibers, the polymers may be present in
ratios of
75/25, 50/50, 25!75 or any other desired ratios. The fibers may also have
shapes such
as those described in US Patents 5,277,976 to Hogle et al.) US Patent
5,466,410 to Hills
and 5,069,970 and 5,057,368 to Largman et al., which describe fibers with
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unconventional shapes.
As used herein the term "biconstituent fibers" refers to fibers which have
been
formed from at least two polymers extruded from the same extruder as a blend.
The
term "blend" is defined below. Biconstituent fibers do not have the various
polymer
components arranged in relatively constantly positioned distinct zones across
the cross-
sectional area of the fiber and the various polymers are usually not
continuous along the
entire length of the fiber, instead usually forming fibrils or protofibrils
which start and end
at random. Biconstituent fibers are sometimes also referred to as
multiconstituent fibers.
Fibers of this general type are discussed in, for example, US Patents
5,108,827 and
5,294,482 to Gessner. Bicomponent and biconstituent fibers are also discussed
in the
textbook Polymer Blends and Composites by John A. Manson and Leslie H.
Sperling,
copyright 1976 by Plenum Press, a division of Plenum Publishing Corporation of
New
York, ISSN 0-306-30831-2, at pages 273 through 277.
As used herein the term "blend" means a mixture of two or more polymers while
the term "alloy" means a sub-class of blends wherein the components are
immiscible but
have been compatibilized. "Miscibility" and "immiscibility" are defined as
blends having
negative and positive values, respectively, for the free energy of mixing.
Further)
"compatibilization" is defined as the process of modifying the interfacial
properties of an
immiscible polymer blend in order to make an alloy.
As used herein, the term "garment" means any type of non-medically oriented
apparel which may be wom. This includes industrial work wear and coveralls)
undergarments, pants, shirts, jackets, gloves) socks, and the like.
As used herein) the term "infection control product" means medically oriented
items such as surgical gowns and drapes, face masks, head coverings like
bouffant
caps, surgical caps and hoods, footwear like shoe coverings, boot covers and
slippers,
wound dressings, bandages, sterilization wraps, wipers, garments like lab
coats,
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coveralls, aprons and jackets, patient bedding, stretcher and bassinet sheets,
and the
like.
As used herein, the term "personal care product" means diapers, training
pants,
absorbent underpants, adult incontinence products, and feminine hygiene
products.
As used herein, the term "protective cover" means a cover for vehicles such as
cars, trucks, boats, airplanes, motorcycles, bicycles, golf carts, etc.,
covers for equipment
often left outdoors like grills, yard and garden equipment (mowers, rato-
tillers, etc.) and
lawn furniture, as well as floor coverings, table cloths and picnic area
covers.
As used herein, the term "outdoor fabric" means a fabric which is primarily,
though
not exclusively, used outdoors. Outdoor fabric includes fabric used in
protective covers,
camper/trailer fabric, tarpaulins, awnings) canopies, tents, agricultural
fabrics and outdoor
apparel such as head coverings, industrial work wear and coveralls, pants,
shirts, jackets,
gloves, socks, shoe coverings, and the like.
TEST METHODS
Cup Crush: The softness of a nonwoven fabric may be measured according to
the "cup crush" test. The cup crush test evaluates fabric stiffness by
measuring the peak
load (also called the "cup crush load" or just "cup crush") required for a 4.5
cm diameter
hemispherically shaped foot to crush a 23 cm by 23 cm piece of fabric shaped
into an
approximately 6.5 cm diameter by 6.5 cm tall inverted cup while the cup shaped
fabric is
surrounded by an approximately 6.5 cm diameter cylinder to maintain a uniform
deformation of the cup shaped fabric. An average of 10 readings should be
used. The
foot and the cup are aligned to avoid contact between the cup walls and the
foot which
could affect the readings. The peak toad is measured while the foot is
descending at a
rate of about 0.25 inches per second (380 mm per minute) and is measured in
grams.
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The cup crush test also yields a value for the total energy required to crush
a sample (the
°cup crush energyu) which is the energy from the start of the test to
the peak load point,
i.e. the area under the curve formed by the load in grams on one axis and the
distance
the foot travels in millimeters on the other. Cup crush energy is therefore
reported in gm-
mm. Lower cup crush values indicate a softer laminate. A suitable device for
measuring
cup crush is a model FTD-G-500 load cell (500 gram range) available from the
Schaevitz
Company, Pennsauken, NJ.
Melt Flow Rate: The melt flow rate (MFR) is a measure of the viscosity of a
polymer. The MFR is expressed as the weight of material which flows from a
capillary of
known dimensions under a specified load or shear rate for a measured period of
time
and is measured in grams/10 minutes at a set temperature and load according
to, for
example) ASTM test 1238-90b.
Grab Tensile test: The grab tensile test is a measure of breaking strength and
elongation or strain of a fabric when subjected to unidirectional stress. This
test is known
in the art and conforms to the specifications of Method 5100 of the Federal
Test Methods
Standard 191A. The results are expressed in pounds to break and percent
stretch
before breakage. Higher numbers indicate a stronger, more stretchable fabric.
The term
"load" means the maximum load or force, expressed in units of weight, required
to break
or rupture the specimen in a tensile test. The term "strain" or "total energy"
means the
total energy under a load versus elongation curve as expressed in weight-
length units.
The term "elongation" means the increase in length of a specimen during a
tensile test.
Values for grab tensile strength and grab elongation are obtained using a
specified width
of fabric, usually 4 inches (102 mm), clamp width and a constant rate of
extension. The
sample is wider than the clamp to give results representative of effective
strength of
fibers in the clamped width combined with additional strength contributed by
adjacent
fibers in the fabric. The specimen is clamped in, for example, an Instron
Model TM,
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PCT/US97/Z3200
available from the Instron Corporation, 2500 Washington St., Canton, MA 02021,
or a
Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instnrment
Co.,
10960 Dutton Rd., Phila., PA 19154, which have 3 inch {76 mm) long parallel
clamps.
This closely simulates fabric stress conditions in actual use.
Trap Tear test: The trapezoid or "trap" tear test is a tension test applicable
to
both woven and nonwoven fabrics. The entire width of the specimen is gripped
between
clamps, thus the test primarily measures the bonding or interlocking and
strength of
individual fibers directly in the tensile load, rather than the strength of
the composite
structure of the fabric as a whole. The procedure is useful in estimating the
relative
ease of tearing of a fabric. It is particularly useful in the determination of
any appreciable
difference in strength between the machine and cross direction of the fabric.
in
conducting the trap tear test, an outline of a trapezoid is drawn on a 3 by 6
inch (75 by
152 mm) specimen with the longer dimension in the direction being tested) and
the
specimen is cut in the shape of the trapezoid. The trapezoid has a 4 inch (102
mm) side
and a 1 inch (25 mm) side which are parallel and which are separated by 3
inches (76
mm). A small preliminary cut of 5/8 inches (15 mm) is made in the middle of
the shorter
of the parallel sides. The specimen is clamped in, for example, an Instron
Model TM,
available from the instron Corporation, 2500 Washington St., Canton, MA 02021,
or a
Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument
Co.,
10960 Dutton Rd., Phila., PA 19154, which have 3 inch (76 mm) long parallel
clamps.
The specimen is clamped along the non-parallel sides of the trapezoid so that
the fabric
on the longer side is loose and the fabric along the shorter side taut, and
with the cut
halfway between the clamps. A continuous load is applied on the specimen such
that the
tear propagates across the specimen width. It should be noted that the longer
direction
is the direction being tested even though the tear is perpendicular to the
length of the
specimen. The force required to completely tear the specimen is recorded in
pounds
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with higher numbers indicating a greater resistance to tearing. The test
method used
conforms to ASTM Standard test D1117-14 except that the tearing toad is
cafcutated as
the average of the first and highest peaks recorded rather than the lowest and
highest
peaks. Five specimens for each sample should be tested.
DETAILED DESCRIPTION OF THE INVENTION
The extnrdable composition of this invention is an alloy of at least two
immiscible
polymers. The alloy of polymers used to make the composition of this invention
is such
that the polymer melt temperature of the non-continuous phase is in the range
of from
less than 30 °C below to any value greater than that of the continuous
phase. The
extrudable composition may be extruded to form fibers which are biconstituent
and the
fibers may be further processed into nonwoven fabrics.
The alloy should be essentially free of any compatibilzer. Compatibilizers
include
compounds such as zinc ionomers of ethylene-methacrylic acid or modified
polypropylene with malefic anhydride and others described in US Patent
5,534,335. It is
believed, though applicants do not wish to be bound by any particular theory,
that a
compatibiiizer has polar and non-polar parts and the polar part reacts with or
is attracted
to a polar part of one of the polymers to be alloyed. The non-polar part of
the
compatibilizer remains available for reaction with or attraction to the
dominant phase
polymer and this results in more intimate mixing. The reduction in the
interfacial energy
caused by the compatibilizer allows the size of the discontinuous phase to be
reduced
within the continuous phase.
Another class of compatibilizer is poly(olefin-methacrylic acid) where the
acid
groups are partially or fully neutralized by metal ions.
Commercial examples of compatibilizers which should be avoided inGude Exxelor~
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polymer modifier P01015 or VA 1803 available from Exxon Chemical Company, and
the
family of Surlyn~ ionomers available from E.I. Dupont de Nemours Inc.,
particularly
Surlyn~ 9020 ionomer.
Exxelor~ polymer modifier P01015 is a proprietary chemical which has a melt
flow
rate of 120 g/10 min., a density of 0.91 g/cm3 and has 0.4 weight percent of
grafted
malefic acidlanhydride. Exxelor~ polymer modifier VA1803 has a melt flow rate
of 3 g/10
min., a density of 0.86 g/cm3 and has 0.7 weight percent of malefic
acid/anhydride.
Surlyn~ 9020 ionomer has a melt flow rate of 1.0 g/10 min. and a density of
0.96 g/cm3.
The Surlyn~ ionomer resins are based on ethylene and methacrylic acid di- and
ter-
polyers which have been partially reacted with metallic salts (generally zinc
or sodium) to
form ionic crosslinks between the acid groups within a chain or between
neighboring
chains.
Suitable polymer mixtures which may be used in the practice of this invention
include, for example, polyolefins and polyamides, and polyolefins and
polyesters.
The polyolefin which may be used in the practice of this invention may be
amorphous or crystalline, atactic) isotactic or sydiotactic. Suitable
polyolefins include
polyethylene, polypropylene, polybutylenes and copolymers) blends and mixtures
thereof
and are available commercially from a number of suppliers. The particular
properties of
polyolefins used in fiber extrusion and nonwoven fabric production processes
such as the
spunbonding and meltblowing processes are known to those skilled in the art.
A polyamide which may be used in the practice of this invention may be any
polyamide known to those skilled in the art including copolymers and mixtures
thereof.
Examples of polyamides and their methods of synthesis may be found in "Polymer
Resins" by Don E. Floyd (Library of Congress Catalog number 66-20811, Reinhold
Publishing, NY, 1966). Particularly commercially useful polyamides are nylon-
6, nylon
6,6, nylon-11 and nylon-12. These polyamides are available from a number of
sources
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such as Emser Industries of Sumter, South Carolina (Grilon~ 8 Grilamid~
nylons),
Atochem Inc.) Polymers Division) of Glen Rock, New Jersey (Rilsan~ nylons),
Nyltech
Industries of Manchester) NH, among others.
Modifying the interfacial properties of the immiscible polymer blend to make
an
alloy is accomplished through the use of high shear mixing through the use of
for
example, a single screw extruder. Single screw extruders ate known in the art
as useful
in mixing and have been developed for a number of purposes in polymer
processing
such as improvement in physical properties, appearance) processibility and
cost
reduction. A detailed description of mixing and single screw extruders is
given in Mixin
and Compounding of Polymers: Theory and Practice, ISBN 1569901562) edited by
I.
Manas-Zloczower and Z. Tadmor, Hanser Publishers) 1994, in chapter 19 (Single
Screw
Extruders), by Hensen, Imping and Spanknebel.
Another method of mixing is by using a commercially available Barmag three
dimensional dynamic mixer (3DD). This mixer is available from Barmag
Aktiengeisellschaft, Leverkuser Strase 65, 42897 Remscheid, Germany, or in the
US
from American Barmag Corporation, 1101 Westinghouse Boulevard, Charlotte, NC
28241.
Figure 1 shows a system suitable for use in the practice of this invention. A
mixture
of polymers in, for example, pellet form, is introduced to the feed hopper 1.
The mixture
proceeds into the main extruder 2 where it is forced through the extruder 2,
passing
through five equally sized heating zones. The melted mixture from the extruder
2 then
passes into the 3DD mixer 3 and is ultimately extruded at the exit 11.
Auxiliary mixing
can be provided by a side extnrder 9 which receives feed from hopper 8. After
exiting
the side extruder 9, the melted mixture is pumped by gear pump 10 into the
main
extruder 2 discharge for mixing in the 3DD mixer 3. Polymers may also be mixed
by
placing them in separate feed tanks 4, 5, pumping them together through
metering
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pumps 6, 7 and then into main extruder 2 discharge for mixing in the 3DD mixer
3.
Yet another method of mixing is by using a cavity transfer mixer (CTM) by
Rapra
Corp. which makes available its mixers in the United States through Davis-
Standard of #1
Extrusion Drive, Pawcatuck, CT 06379 which may be used in place of a 3DD
mixer. A
CTM mixer is shown in Figure 2 which shows a central shaft 12 which is
surrounded by a
housing 13) 14 divided in two parts for ease of illustration. The housing 13)
14 is
stationary and the shaft 12 rotates in actual use. The rotation of the shaft
12 causes
polymer to be forced into and out of the multitude of depressions 15 on the
shaft 12 and
housing 13, 14) causing good mixing. While the depressions 15 shown in Figure
2 are
circular, many other shapes are possible. The 3DD mixer uses rectangular, slot-
like
depressions. Rhomboid, triangular and any other shape which may be envisioned
may
be used. ft is also possible to use pins instead of depressions and to place
the pins or
depressions at various angles.
Figure 3 shows a cross-sectional view of a mixer. The shaft 16 and housing 17
have depressions 18. Polymer may enter at the inlets 19, 20 and move to the
discharge
21.
Distributive an dispersive mixing are essential in any good mixing or
blending.
Distributive mixing involves the homogenization of the dispersed particles in
the matrix
material. Dispersive mixing is a mechanism whereby large particles (dispersed
phase)
are broken up into finer particles and are evenly distributed throughout the
matrix
material. Important parameters for mixing are constancy of temperature,
pressure and
above all viscosity. The viscosity homogeneity gives information about
distributive and
dispersive mixing.
The fibers which may be made from the extrudabfe composition of this invention
may be produced by the meltblowing or spunbonding processes which are well
known in
the art. These processes generally use an extruder to supply melted polymer to
a
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spinneret where the polymer is fiberized. The fibers are then drawn, usually
pneumatically, and deposited on a foraminous mat or belt to form the nonwoven
fabric.
The fibers produced in the spunbond and meltblown processes are generally in
the range
of from about 1 to about 50 microns in diameter, depending on process
conditions and
the desired end use for the fabrics to be produced from such fibers.
The fibers may also have other polymers present in a conjugate structure
wherein
the biconstituent blend of this invention makes up one portion of the
conjugate fiber, e.g.
the sheath or core, and another polymer or blend makes up the other portion.
Fabric made from fibers of the extrudable composition of this invention may be
used in a single layer embodiment or as a component of a multilayer laminate
which may
be formed by a number of different laminating techniques including but not
limited to
using adhesive, needle punching, thermal calendering and any other method
known in
the art.
The following examples illustrate particular embodiments of the invention.
EXAMPLE 1
The polymer alloys were generally produced by compounding the ingredients in a
cement mixer which should have given a relatively poorly homogenized mixture.
The
polyolefin used was Union Carbide's E5D47 polypropylene, a 38 g/10 min melt
flow rate
polymer. The polyamide used was a polyamide 6 sold as Nyltech 2169 by Nyltech
Industries.
The amounts in the initial blends were 2.2 weight percent polyamide, 2.0
weight
percent titanium dioxide pigment and the balance polypropylene.
The alloy was melt spun through a standard 600 hole round pack with a pin
density
of about 125 holes per inch (hpi), a length to exit diameter (UD) of 6 and a
0.6mm exit
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diameter. The extruder and spinpack temperatures were at about 440°F
(227°C) and
450°F (232°C) respectively and throughput was typically 0.7
grams/hole/min (ghm). No
mixer was attached to the extruder discharge so the extruded polymer went
directly to
the spinpack. The extruded fibers were thermally point bonded by calendering
using an
Expanded Hansen Penning bond roll with a 15% bond area to create a fabric with
integrity at a calender temperature of 283°F (139°C} as
indicated in Table 1.
Mechanical data for 2 ounce per square yard (osy) (68 gsm) spunbond fabrics
made from these alloy fibers is shown in the Table in relation to a control
fabric made
from fibers of Union Carbide's E5D47 polypropylene alone, and shows an
improvement
in properties of interest.
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TABLE 1
. Value Std. Dev.,Value Std. Dev.,
of of
Test Units Control Control Example Examale Ratio
Basis Wt. Osy ~ 2.05 0.03 2.09 0.07 0.98
Strip
Tensile
Peak load pounds 11.36 0.29 24.49 0.98 116
Strain percent 27.51 2.99 116.79 16.78 324
Energy in-Ib. 8.08 1.66 80.86 14.77 901
Grab
Tensile
Peak load pounds 12.56 0.97 27.19 2.86 116
Strain percent 68.17 11.01 108.64 13.75 ~ 59
Energy in-Ib. 16.91 4.42 53.30 12.48 215
Trap Tear
1'~ peak pounds 6.21 0.54 14.46 1.71 133
Cup crush
load grams 285.02 13.17 262.21 36.28 8
The two fabrics were tested for dyeability by dipping each for one minute in
boiling
water containing 1 weight percent of Dupont Fiber Identification Stain #4..
After the
minute of boiling, the fabrics were rinsed in clean water until no dye was
visible in the
rinse water) and then dried on blotting paper. The stain is available from
Pylan Products
Co. Inc., 1001 Stewart Ave., Garden City) NY 11530. It was found that the
polypropylene
fabric did not accept any stain while the biconstituent fiber accepted the
stain, indicating
that polyamide was available at the fiber surface and not entirely embedded in
the
polypropylene matrix.
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EXAMPLE 2
A single screw extruder was used having a CTM mixer attached to its discharge.
The screw had a length of 13.5 feet (411.5 cm) and a diameter of 4.5 inches
(11.4 cm)
and was charged at a rate of about 180 pounds/hour with a mixture of Exxon
Chemical's
Escorene~ 3445 polypropylene and Nyltech 2169 nylon 6. The extruder discharge
was
fed into the CTM which operated at a temperature of about 460 °F (238
°C). The mixture
was processed into fibers at a rate of 0.70 grams/hole/minute (ghm) with 0.6
mm holes
and bonded using an expanded Hansen-Pennings pattern (EHP). Up to 3 weight
percent
polyamide was processed using this configuration.
EXAMPLE 3
A 30 mm diameter co-rotating twin screw extruder was used having a Barmag 3DD
mixer attached to its discharge. It was charged at a rate of about 100
pounds/hour with
Escorene~ 3445 polypropylene. The extruder discharge was fed into the 3DD
which
operated at a temperature of about 482 °F (250 °C). Nylon was
added to the 3DD intake
at varying rates. The mixture was processed into fibers and drawn by passing
over a first
and second godet at rates of 900 and 2800 m/min so that the fibers were
stretched at a
3:1 ratio between the godets. Trials were conducted at from 3.4 to 15 weight
percent
nylon in the polypropylene fibers. Fibers processed well until the 15 percent
nylon rate
where fibers were breaking, but the nylon addition was reduced to 13 percent
and then
processed well again.
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EXAMPLE 4
A 30 mm diameter co-rotating twin screw extruder was used having a Barmag 3DD
mixer attached to its discharge. The screw was charged at a rate of about 100
pounds/hour with a mixture of Escorene~ 3445 polypropylene and nylon. The
extruder
discharge was fed into the 3DD which operated at a temperature of about
482°F (250
°C). The mixture was processed into fibers and drawn by passing over a
first and second
godet at rates of 900 and 2800 mlmin so that the fibers were stretched at a
3:1 ratio
between the godets. Trials were conducted using 5 and 10 weight percent nylon
in
polypropylene dry blended in a cement mixer and fed into the main extruder
feed with no
side stream addition. Fibers processed well and were stable at both the 5 and
10 weight
percent rates.
Although only a few exemplary embodiments of this invention have been
described
in detail above, those skilled in the art will readily appreciate that many
modifications are
possible in the exemplary embodiments without materially departing from the
novel
teachings and advantages of this invention. Accordingly, all such
modifications are
intended to be included within the scope of this invention as defined in the
following
claims. In the claims, means plus function claims are intended to cover the
structures
described herein as pertorming the recited function and not only structural
equivalents
but also equivalent structures. Thus although a nail and a screw may not be
structural
equivalents in that a nail employs a cylindrical surface to secure wooden
parts together,
whereas a screw employs a helical surface, in the environment of fastening
wooden
parts, a nail and a screw may be equivalent structures.
It should further be noted that any patents, applications or publications
referred to
herein are incorporated by reference in their entirety.
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